Facts about the Asian Giant Hornet (05/14/20)

If you’ve read the news recently, and we’re sure you have, you’ve likely seen stories about an exotic and potentially invasive insect called the Asian giant hornet (Vespa mandarinia) or, as has been popularly reported in the media, ‘murder hornet’.

If you’ve read the news recently, and we’re sure you have, you’ve likely seenstories about an exotic and potentially invasive insect called the Asian giant hornet (Vespa mandarinia) or, as has been popularly reported in the media, ‘murder hornet’. It’s big, it packs a powerful sting, and it preys on honey bees (though not exclusively), but perhaps it’s the ‘murder’ moniker that’s gotten the public’s attention. Furthermore, any invasive insect is cause for concern, simply because of the economic and environmental loss that can occur, such as ash tree loss from the emerald ash borer and crop, tree and lawn damage from the Japanese beetle. For beekeepers in North America, the Asian giant hornet could prove costly indeed if it becomes established. Here, we’ll get to the facts about the Asian giant hornet.

Asian giant hornet (Figure 1) is native to tropical and temperate areas of southern and eastern Asia. Asian giant hornet was detected near Vancouver, British Columbia, in August of 2019. The nest was found and eradicated in September. In August and again in October, a beekeeper near Bellingham, WA, saw hornets near house (August) and attacking a hive (October), but the hornet species was not confirmed. In December of 2019, a homeowner near Blaine, WA collected a dead hornet that was later confirmed as Asian giant hornet. These detections prompted a prudent response from the Washington State Department of Agriculture and Washington State University Extension. A concerted effort with Washington beekeepers, who would be the most likely group to encounter the hornets, has not result in any new detections. At present, there are no known established populations of Asian giant hornet in North America. How the hornets were introduced to British Columbia and Washington remains unknown, but according to USDA-APHIS it is possible they arrived as illegal imports for food or medicinal uses. Early detection and response is critical. Public education and monitoring efforts for Asian giant hornet continues. The fact that no further detections occurred this April, when overwintered females begin to emerge, is good news but is not conclusive, as queens are difficult to detect because there are so few of them. Workers are more numerous, and are active in the summer and fall months. Only queens can disperse to form new nests.

Asian giant hornets are predators of other insects, especially bees in the genus Apis, to which our common western or ‘European’ honey bee (Apis mellifera) belongs. Asian giant hornets send out scouts from the nest to find bee hives, and once they do the scouts place pheromone markers for other hornets to follow. Asian giant hornets utilize bee pupae and larvae as food, but kill the adult bees and then guard their new food source aggressively. These hornets are heavily sclerotized, and bees can’t sting through the hornet’s integument. It takes only a few hornets a few hours to kill all of the adults and take over a bee colony. The Japanese honey bee (Apis cerana) has evolved an interesting defense mechanism. Japanese honey bees can detect the hornet’s pheromone and follow it back to the hornet nest where perhaps one hundred bees ambush a hornet scout, form themselves into a tight ball around the hornet, and vibrate their wings vigorously to raise the temperature around the hornet to over 115F, which ultimately kills the hornet. Unfortunately, the European honey bee has no natural defense against the Asian giant hornet. That’s why it’s such a concern for beekeepers, who are already dealing with substantial colony losses due to varroa mites and other stresses.

Asian giant hornet is the world’s largest hornet, with females attaining lengths of nearly 2½ inches. Because of their large size, Asian giant hornets can deliver more venom than smaller hornets, and like other hornets, can sting repeatedly. However, even in its native range human deaths due to Asian giant hornet stings are quite rare, and most are due to allergic reaction, although multiple stings (more than 30) from multiple hornets could potentially deliver a lethal dose of venom. Asian giant hornet is not usually aggressive, and encounters occur when the hornets are defending their nests or their food sources. Here in the United States, about 60 deaths occur each year due to bee, wasp and hornet stings according to the Center for Disease Control and Prevention.

Asian giant hornet is highly unlikely to occur here in North Dakota. The largest wasp or hornet in North Dakota is the eastern cicada killer (Figure 2), which can reach nearly 2 inches in length. Female cicada killers provision their nests with cicadas, and are not aggressive.

The bottom line is that there is no immediate concern about Asian giant hornet occurring in North Dakota, and there is no threat to the public. We ask beekeepers, especially those returning to North Dakota from the Pacific Northwest, to remain vigilant and report any potential sightings and send any suspect specimens to the NDSU Plant Diagnostic Lab for species determination.

For more fact-based information, including resources we used for this article, please consult the following:

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.